A die-casting die not only determines the shape of a die-cast product by its cavity forming surface, but also comprises a function of cooling molten material. If the cooling effect on the molten material caused by the die-casting die is too low, a long time is needed until the molten material cools and the shape of the die-cast product is determined. Furthermore, it becomes impossible to obtain an intended crystal configuration (solid structure) in the die-cast product. On the other hand, if the cooling effect on the molten material caused by the die-casting die is too high, the molten material does not flow readily within the cavity, and it becomes difficult to fill the molten material into the cavity. Furthermore, high injection pressure is needed to fill the molten material into the cavity.
In Japanese Patent Application Publication No. 1996-318362 and Japanese Patent Application Publication No. 1995-155897, a technique is taught in which a die-casting die is composed of a plurality of members, and a thermal conductivity of the die-casting die can be changed depending on location by changing the material used to form the members.